This invention relates in general to freezing point depressant compositions and processes, and in particular to a process for producing a deicing/anti-icing fluid from a byproduct stream.
Processes for producing alkyl esters often produce a byproduct stream in addition to the esters. For example, biodiesel fuel (fatty acid alkyl esters) is typically produced by transesterifying a triglyceride with an alcohol to yield the esters and glycerol. The esters are separated, and a byproduct stream from the process contains the glycerol, water, alkali catalyst, alcohol, free fatty acids (FFAs) and other byproducts of the reaction. The byproduct stream can be subjected to additional processing steps to separate and purify the glycerol. The biodiesel process is described in a publication by Zhang et al., “Biodiesel production from waste cooking oil: 1. Process design and technological assessment”, Bioresource Technology, vol. 89, pp. 1–16 (2003).
Deicing/anti-icing fluids are used in many applications, such as on roadways, sidewalks, airport runways, aircraft exteriors, and other outdoor surfaces where icing is a problem. Deicing involves the application of a deicing fluid onto ice that has already formed on the surface in order to remove the ice; the deicing fluid lowers the freezing point of the ice so that it becomes a liquid rather than a solid. Anti-icing involves the application of an anti-icing fluid onto a surface before ice is present, thereby lowering the freezing point of any precipitation that contacts the surface and preventing it from turning into ice. The term “deicing/anti-icing fluid” refers to a fluid that functions as a deicing fluid and/or an anti-icing fluid. The deicing/anti-icing fluids usually contain water, a freezing point depressant, and appropriate additives. Some commonly used freezing point depressants include propylene glycol, ethylene glycol, and salts such as potassium acetate, sodium acetate, sodium chloride, calcium chloride and sodium formate.
U.S. Pat. No. 6,540,934 assigned to METSS, issued Apr. 1, 2003, discloses deicing/anti-icing fluids containing a monocarboxylic acid salt such as potassium acetate. The patent states that glycerol can also be added to inhibit corrosion.
U.S. Pat. No. 6,596,189 assigned to General Atomics, issued Jul. 22, 2003, discloses deicing fluids containing a mixture of alkaline earth metal and alkali metal carboxylates (such as acetates) along with an aliphatic alcohol.
U.S. Pat. No. 4,448,702 assigned to Lang & Co., Chemisch-Technische Produkte Kommanditgesellschaft (Vienna, AT), issued May 15, 1984 discloses the use of succinic acid and other dicarboxylic acid salts for deicing.
U.S. Pat. No. 6,287,480 assigned to Michigan State University, issued Sep. 11, 2001 discloses deicing compositions which are suitable and effective for airport applications and which inhibit the corrosive effects of conventional road salt. The subject discloses deicing compositions comprising succinate salts.
U.S. Pat. No. 6,623,657 assigned to Michigan State University, issued Sep. 23, 2003, discloses deicing compositions including either succinic acid or succinic anhydride, and a neutralizing base such as sodium hydroxide, potassium hydroxide or ammonium hydroxide. The deicing compositions when mixed with water produce succinate salts in a reaction that rapidly releases sufficient heat to melt the ice on the surface and the succinate salts act as a deicer and freezing point depressant. The deicing compositions can further include a glycol that inhibits the formation of the ice on the deiced surface.